Method op extracting gold



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ALBERT W. SMITH, OF CLEVELAND, OHIO.

METHOD OF EXTRAGTING GOLD.

icense.

No Drawing.

To all whom it may concern:

Be it known that I, ALBERT W. SMITH, a citizen of the United States, and a resident of Cleveland, county of Cuyahoga, and State of Ohio, have invented a new and useful Improvement in Methods of Extracting Gold, of which the following is a specification, the principle of the invention being herein explained and the best mode in which I have contemplated applying that principle, so as to distinguish it from other inventions.

One of the difficulties encountered in the practice of the so-called cyanid process of extracting the precious metals from gold and silver ores, has been the accumulation of detrimental impurities in the cyanid solution, such as sulfo-cyanid, sulfids and ferro-cyanids. Although these accumulate slowly, they tend to prevent ordinary mill cyanid solution from extracting the precious metal in a satisfactory manner. Such impurities, more particularly occur where refractory ores are being dealt with, that is, ores containing tellurids, sulfids, or arsenids of the base metals in such an amount as to render such ores commercially unavailable for the current cyanid treatment.

I am aware that it has been attempted heretofore, to oxidize the foreign substances mechanically combined with the ore, by the use of oxidizing agents, and thereby cause such substances to split off or separate from the precious metals. 1 have discovered, however, that not all oxidizing agents will operate to this end, for while the action of the cyanid involves the use of oxygen, and hence the addition of such oxidizing agents in any form might seem beneficial, this, as a matter of fact is not the case. In other words, a too strenuous oxidizer will not merely reduce the deleterious substances, but also destroy the cyanid by oxidizing it into the cyanate, which is not a solvent for gold.

The object of the present invention, accordingly, is to provide a process whereby the formation of the aforesaid deleterious compounds may be prevented, without directly affecting in any way the action of the cyanid, the greater part of the oxygen for the reaction of the cyanid with the gold being preferably secured by agitating the solution in air as heretofore.

To the accomplishment of the foregoing and related ends, the invention, then, con- Specification of Letters Patent.

Application filed August 15, 1911.

Patented Aug. 1, 1916.

Serial No. 644,161.

sists of the steps hereinafter fully described and particularly pointed out in the claims.

The following description sets forth in detail one approved method of carrying out the invention, such disclosed mode, however, being merely illustrative of the various Ways in which the principle of the invention may be used.

In this preferred procedure, which has been actually carried out in practice, the ore is first crushed dry to pass through a sieve of about one-half inch mesh, and is then ground in a solution of potassium cyanid and potassium bromate to such a fineness that it will pass through a 10-mesh sieve. About one pound of cyanid and one-half pound of bromate are used per ton of solution, and sufficient lime, that is calcium oxid or hydrate, added to keep the solution at all times distinctly alkaline. This solution is employed in the proportion to two or three parts to one of the ore. After being thus ground the mixture of ore and solution is put into a tube mill and ground still finer or slimed. Next it is passed through a classifying machine, arranged to float ofi all particles ground finely enough to pass through a 200-mesh sieve, or one of approximately that fineness. The coarser particles are returned to the tube mill to be ground over again until they are of the proper fineness. From this classifying machine, the solution with the floating material is conducted into a tank which may be termed a thickener, such solution being allowed to stand in said tank so as to permit the finely ground ore to settle in the form of a mud, while the clear solution is conducted back again for use in the preceding steps of the process, as just described. The mud from such thickener-tank then goes through an agitating tank where it is agitated with air for from six (6) to seventy-two (72) hours, further cyanid, bromate and lime being added, if necessary, in order to keep the solution up to'its original strength and alka' linity. The mixture, or pulp, from such agitating tank, is filtered, the solid part washed and then discarded. The extracted gold will then be found in the solution from which it may be separated out as in the current practice of the cyanid process.

A bromate, when employed as above de scribed, I have found serves admirably in keeping the cyanid solution free from detrimental impurities such as sulfo-cyanid, sulfids and ferro-cyanids previously referred to. The action of the bromate, however, is not strenuous enough to destroy the cyanid so that the latter may perform its proper function of dissolving the precious metal when the mixture is agitated preferably with air, as previously stated. The bromate has been found a satisfactory oxidizing agent also in that it does not retard or prevent the action of the zinc used in finally precipitating the gold from the solution.

It has perhaps been already sufficiently indicated that my improved process is not of necessity limited to the treatment of auriferous ores, butmay be applied to the extraction of silver from silver-bearing ores as Well. The specific reference, accordingly in the description above given, to gold, is not to be construed as a limitation, and in general the terms, gold and silver, as herein used are to be understood as interchangeable. Furthermore, while in the specific illustration thus given, the tri-oxy salt of bromin is described as being employed, iodin and the alkaline salts of the oxy-acids of iodin have also been found to give satisfactory results; that is, while they do not oxidize the cyanid, they do prevent the formation of the objectionable substances previously mentioned. Potassium cyanid and sodium cyanid are, of course, well known equivalents in the cyaniding step, and as a matter of fact in the cyanid method of gold extraction as at present practised the latter is now the more generally used.

Other modes of applying the principle of my invention may be employed instead of the one explained change being made as regards the process herein disclosed, provided the step or steps stated by any one of the following claims or the equivalent of such stated step or steps be employed.

I therefore particularly point out and dis tinctly claim as my invention 1. In a method of extracting precious metals from their ores, the steps which consist in treating'the ore with a solution of cyanid and an oxy-halogen compound, and maintaining such solution alkaline throughout the reaction.

2. In a method of extracting precious metals from thelr ores, the steps which consist 1n treatlng the ore with a solution of cyanid and an oxy-bromin compound, and

maintaining such solution alkaline throughout the reaction.

3. In a method of extracting precious metals from their ores, the steps which consist in treating the ore with a solution of cyanid and a bromate, and maintaining such solution alkaline throughout the reaction.

4. In a method of extracting precious metals from their ores, the steps which consist in treating the ore with a solution of cyanid and a bromate, and adding lime to such solution in amount suflicient to maintain the same distinctly alkaline throughout the reaction.

5. The method of extracting precious metals from their ores, which consists in finely grinding the ore with a solution of cyanid and an oxy-halogen compound; maintaining such solution alkaline throughout the reaction; and then agitating the mixture with air.

6. The method of extracting precious metals from their ores, which consists in finely grinding the ore with a solution of cyanid and a bromate; adding lime to such solution in amount sufiicient to maintain the same distinctly alkaline throughout the reaction; and then agitating the mixture with air.

7, In a method of extracting gold and the like from refractory ores, the step which consists in treating the ore, in finely ground condition, with a solution of potassium cyanid and potassium bromate in the presence of lime.

8. In a method of extracting precious metals from refractory ores, the steps which consist in finely grinding the ore in solution with potassium cyanid and potassium bromate in the presence of lime, and then agitating the mixture with air.

Signed by me this 10th day of August,

ALBERT W. SMITH. Attested by- MYRTLE K. SCI-IUCII, JNo. F. OBERLIN.

Copies of this patent may be obtained for five cents each, by addressing the Commissioner of Patents,

' Washington, D. 0. 

